The objective of this proposal is to study the mechanism of smooth muscle differentiation in the prostate through an intricate cell-to-cell interaction. The following is our hypothesis. During development, stroma of the fetal prostate is populated by fibroblasts. Smooth muscle cells are not present until day 18 of gestation. As they appear, they are located only around the epithelial cells. This observation strongly suggests that epithelial cells facilitate the conversion of fibroblasts into smooth muscle cells. Two events likely triggered by epithelial cells are the induction of aromatase and estrogen receptor in the stroma. This is critical since estrogen can induce smooth muscle phenotype. Finally, we postulate that androgen and estrogen actions are mediated through TGFbeta action in smooth muscle differentiation. Three specific aims are proposed. Specific Aim 1 is to study the effect of epithelial cells on stromal cells. We hypothesize that prostatic epithelial cells possess the potential to induce the expression of aromatase and estrogen receptor in the stroma. Prostatic epithelial cells consist of at least two cell types: basal cells and luminal cells. It remains unclear which cell type has the ability to induce these events. We propose to develop rat prostatic epithelial cultures with either predominant basal cells or luminal cells. This will provide the opportunity for us to evaluate which cell type will have an impact on smooth muscle cell differentiation. Specific Aim 2 is to study the effect of androgen and estrogen on stromal cells. Both androgen and estrogen have a profound effect on prostatic stromal cells. We postulate that estrogen induces the smooth muscle phenotype; while androgen maintains the differentiated phenotype. However, the exact division of responsibility between androgen and estrogen in smooth muscle differentiation remains unclear. We propose to use prostates of neonatal rats, neonatal estrogenized rats, and estrogen receptor knockout mice as models to study smooth muscle differentiation. Specific Aim 3 is to study the effect of transforming growth factor-beta on stromal cells. In cultures of human prostatic stromal cells, TGF- beta induced a smooth muscle phenotype. Both androgen and estrogen induce TGF-beta expression in prostatic stromal cells. We hypothesize that the action of androgen and estrogen in smooth muscle differentiation is mediated through the action of TGF-beta. We propose to use a dominant negative type II TGF-beta receptor (TbetaRII-DN) expression vector to render cells insensitive to TGF-beta. We also will study the prostate of TGF-beta1 knockout mice.